Functional Safety Assessment FSA

A functional safety assessment is an investigation of the ability of an SIF to achieve the necessary functional and integrity requirements. The investigation is based on the evidence available at the time of the assessment. As the lifecycle progresses, more evidence is available for examination. 

The Stage 3 FSA should be completed prior to introduction of hazardous materials into the process. ANSI/ISA-84.00.01-2004-1, Clause 5.2.6.1.2, does require that at least one senior, competent, independent (from the main project team) person take part in the FSA. This competent person should be able to review the hazard and risk analysis, design, implementation, and testing to ensure that everything had been successfully completed. This senior person should also have the authority to prevent the start-up of the process unit if necessary. 

If the assessment team feels the SIF has not been properly designed, installed, or validated, they should escalate their finding to senior management. Likewise, if they discover testing procedures have not been written or personnel have not been properly trained, these findings should also be forwarded to the plant senior management. 

Although the standard (consistent with OSHA 1910.119) only mandates the Stage 3 FSA, many companies elect to conduct similar assessments after the other four stages. They also have specific requirements for the composition of the assessment team and its independence from the project team. 

Functional Safety Assessments can utilize checklists to facilitate the assessment at the various lifecycle stages. This qualitative assessment is a continuous process carried out at each life-cycle phase, i.e., specification, design, manufacture, commissioning and operation of the system. The use of a checklist ensures that  

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The use of Functional Safety Assessment (FSA) is fundamental in demonstrating that a Safety Instrumented System (SIS) fulfils its requirements regarding safety instrumented function(s) and Safety Integrity Level (SIL).... The following attributes are considered good practice for Functional Safety Assessment ... 

SIL is a dependability measure of the overall safety function performed by the safety system in question. So, it is necessary that all critical attributes of a device are stated in the certificate to indicate suitability of the device in SIL-rated safety functions. SIL is not just the probabilistic failure data. Also note that the SIL number mentioned in a certificate is normally arrived at after a number of assumptions on overall safety and conditions required for SIL allocation. In fact, lEC 61508 does not directly mention requirements for certificates instead it puts more importance on functional safety assessment (FSA). 

There seems to be a lot of duplication in the validation type of activities but in practice each serves a different purpose. Functional Safety Assessment (FSA) is defined in a separate clause in lEC, clause 8. 

From the preceding, it is clear that SIS and reliability go hand-in-hand. A functional safety assessor (FSA) assesses the safety assessment/analysis report (SAR) after SIS is developed to check the system reliability and SIL. In order to achieve a tolerable risk level, the end-user, who needs to install SISs in the plant, initiates SIS projects. Detailed process outline for the same has heen elaborated as follows ... 

Part 1 clause 8 of lEC 61508 (Functional Safety Assessment) addresses this area. FSA should be done at all lifecycle phases (not just Phase 9, Realization). There are minimum levels of independence of the assessment team from the system/eompany being assessed, depending on the SIL involved. In summary these are ... 

Anticipating the requirement for FSA services the established certifying organizations already offer FSA services. In the UK a new company has been formed to specialize in providing training for conformity assessment and has taken the name The CASS Scheme Ltd . The implications of this scheme are that competency guidelines and training schemes are in place for persons to be trained as Functional Safety Assessors. 

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